Oscillation generator circuit



March 5, 1940. R. H. SIEMENS 0 OSCILLATION GENERATOR CIRCUIT Filed March 30, 1957 2y SheetsSheet 1 )0 Z fil K I INVENTOR RIF/SIEMENS ATTORNEY March 5, 1940. Q S' v 2,192,205

OSC ILLATION GENERATOR CIRCUIT Filed March so, 1937 g Sheets-Sheet 2 l AAAAAAA "'Y'" INVENTOR v R. H. SIEMENS ATTORNEY Patented Mar. 5, 1940 1 OSGILLATIO-N GENERATOR CIRCUIT Rudolph H. Siemens, Richmond Hill, N. Y., as-

signor to Radio Corporation of America, a

corporation of Delaware Application March 30, 1937,, Serial No. 133,753

11 Claims. (Cl. 250-36,)

This invention relates to oscillation generator --'cir'cuits, and more particularly to such circuits as the two-terminal oscillator type. By the expression two-terminal oscillator, as understood ,5 1 in engineering practice, is meant a generator em- "ploying only a single 'tuned circuit whose two 1 terminals are required to be connected to the generator for producing an operative structure.

Heretofore, in oscillator circuits designed to "10 cover various frequency ranges, it has been necessary to switch a plurality of contacts in order to change from one frequency range to another. Such arrangements, besides being relatively expensive and cumbersome, are rather complicated l and introduce undesirable energy losses.

The present invention, inter alia, overcomes the foregoing disadvantages I and provides a relatively simplified oscillation circuit. which requires that only'one contact be changed in order to switch 1 20 from one frequency range to another.

Accordingly, one of the objects of the present invention is to provide. a simplified oscillator wherein a minimum of switching of tuned circuitsis required for obtaining a number of different frequency ranges.

' Another object is to provide a simplified regenerative'type of two-terminal oscillator where- 1 in a vacuum tube is employed to replace the usual feed-back coil. 30 -A further object is to provide a multi-tube regenerativeoscillator in which direct coupling is employed between the output electrode of one tube and the input electrode of the succeeding tube, and use made of this direct coupling to provide bias for said input electrode.

. 5 the tubes of the oscillator may be operated over substantially linear portions of their respective grid 1 voltage-grid current characteristics, thus producing oscillations which are substantially free from undesired harmonics.

' 50 Other objects, features and advantages will appear from a reading of the following description, taken in conjunction with the accompanying drawings, wherein Figs. 1 to 6, inclusive, illustrate different embodiments of an oscillation generator 65 circuit constructed in accordance with the prin ciples of the present invention. In these figures,

like parts are indicated by like reference numerals.

Referring to Fig. 1 in more detail, there is shown a two-terminal multi-tube high frequency 5 oscillator comprising a pair of tubes T1 and T2. Although tubes T1 and T2 are here shown as being of the triode type, it is to be distinctly understood that, if desired, such tubes may have additional electrodes. 1 Vacuum tube T1 includes, among its electrodes, a grid G1, a cathode K1 and an anode P1. Coupled to the grid G1 and cathode K1 is a tuned oscillatory circuit comprising an inductance L1 having in shunt therewith a variable condenser C4. A switch S is provided for enabling, alternatively, the selection of any one ofa plurality of other coils L2, L3 etc., for cooperating with the condenser C4 for obtaining a change in the frequency range of the oscillator. The usual grid-leak and condenser combination 2 here shown by the reference numerals R2 and C1 provide the automatic-bias for the input electrode G1 of the tube. Conductively coupled to the anode P1 through a direct connection M is a grid G2 of a vacuum tube T2 whose anode P2 is coupled back to the input circuit L1, 04 through connection N for providing feed-back of energy.- The feed-back of energy from the output electrode of tube T2 to the input electrode of tube T1 is insuch phase and of such magnitude as to overcome thelosses in the. circuit and produce oscillations. Putting it another way, it may be said that the voltage gain of the two tubes T1 and. T2 is, unity or'greater between grid G1 of tube T1, and the anode P2 of tube T2.

Directly connected to the connection M, there is shown a resistance R3 which acts as a load for the anode P1, and simultaneously provides grid bias for the grid G2. An inductance L1 is arranged in series. with R3 and is of such value as 40 to correct for the phase shift occurring in the load circuit R3. A radio frequency by-pass condenser C3 connects the cathodes of the two tubestogether, in the manner indicated in the drawing.

The usual source of potential indicated at 3+ is I connected to the lower terminal of coil L1 for maintaining the anodesP1 and P2 of the tubes at a positive potential relative to their respective cathode. The path of the positive source 3+ for the anodes of the tubes may be traced through resistance R1, through inductance L1, switch S, and feed-back path N to the anode P2. The positive polarizing potential for the anode P1 is obtained through tube T2, "over the cathode K2 and its connection to the lower terminal of inductance L4, and resistance R3. It will be obvious that there will be a difference in the magnitude of the polarizing potentials applied to the anodes P1 and P2 due mainly to the voltage drop in the tube T2. In one embodiment actually used in practice, the voltage applied to the source B+ was 250 volts. The magnitude of the voltage applied to the anode P1will be less than that applied to the anode of tube T2, .with respect to ground or the negative terminal of the anode supply, the difference varying in accordance with the amount of grid bias on the electrodes of the tubes. A radio frequency by-pass and blocking condenser C2 is connected between the anode source 3+ and the cathode of the tube T1 for preventing a direct path for the current from the positive source 3+ to ground. Condenser C2 also completes the tuned circuit between the lower end of C4 and L1,

L2, L3, etc. This condenser C2 in conjunction with R1 forms a filter isolating the oscillator circuit from other circuits'which may be connected on the same power supply system.

The operation of the circuit is as follows. Any voltage appearing across thetuned circuit L1, C4

impressed across the grid G1 and the cathode K1 of the tube T1, whereupon it developes'a voltage on the anode P1 substantially 180 outof phase with the original voltage which is then transmitted to the grid G2 by the connection M.

The tube T2 functions as an amplifier and produces on the anode P2 a voltage which is again reversed substantially 180 with respect to the voltage on the grid G2, but now in phase with.

the original voltage on grid G1. It will thus be seen that the tube T2 serves both as an amplifier and as a phase inverter. By suitably selecting the constants of the circuit, any desired degree of amplification of the original exciting impulse may be obtained.

Fig. 2 illustrates an identical circuit arrangement as that shown in Fig. 1, the electrodes of both tubes being contained within a single envelope. Since the connections of Fig. 2 are similar in every respect with those of Fig. 1, and the operation of the oscillator is the same, it is not believed necessary to repeat what has been said before. In one oscillator actually constructed in accordance with the circuit of Fig. 2, there was used an RCA type 6C8 dual triode. With such a tube, oscillations as high as 38 megacycles were obtained. This frequency is givenby way of example, merely to indicate the possibilities of the circuit, but it does not represent the limit to which the oscillator of the invention can be operated.

In a dual tube where a common cathode is employed for the two grids and their respective anodes, such as in the RCA type 6N7, a circuit such as shown in Fig. 3 may be used instead of that shown in Fig. 2. Besides using a common'cathode, Fig. 3 differs from Fig. 2 11121111 1 in the use of a buckingbattery F inserted in the lead M, the battery being so polarized as to provide the correct operating bias for the grid shown in the upper section of the envelope of the tube. An additional source of anode supply B+ is employed to supply potential to the anode of the lower portion of 'the tube, which anode corresponds to respect to the common cathode. The operation of this circuit is substantially identical with that of Figs. 1 and 2.

Fig. 4 illustrates another embodiment of 211 oscillation generator in accordance with the principles of the present invention. The operation of this circuit is substantially the same as that of .the other figures with. the. addition of. an auto-' may be employed. The automatic amplitude reg-- ulator feature consists of a connection from the grid G1 of the triode portion of the tube to the grid G2 of the pentode portion. This connec-' tion includes a resistance-condenser filter network R7, Cs and a resistor R5. The pentode screen gridportion of the tube is usedin order to obtain a.wiole range of control of the voltage amplification of this portion of the circuit, because of the automatic amplitude regulator feature. Itshould be noted that the pentode portion of this tube;

' includes a screen gIidGs and a. suppressor grid G1, the screen grid being supplied with a-.suitable positive potential from a source of supply 13.

The automatic amplitude regulator feature functions as-follows: Assuming that the oscilla tion generator is generating oscillations of a certain amplitude, then a voltage will appear across the resistance R2 due to the current drawnxby.

The condenser C7 serves to isolate the anode P1 from the grid G2 fordirect current. o

the grid G1. This Voltage will be polarized negaing on this last grid. is essentially the. same as: that on the grid G1. This amount of-potentialon the grid G2 will allow the tube to function with a certain voltage amplification. If the oscil-v lator now tends to oscillate more strongly, a larger potential will; be developed acrossthe resistance R2 which, in-turn, is passed to the condenser Cs charging it more negatively than be- I fore, and thus a morenegative potential will in turn be passed on to grid G2. Because of the" action of the variable mu pentode portion of the tube, the gain of this portion of' the circuit'will be reduced from that formerly obtainedwhen the oscillation generator was generating voltage of lower amplitude, thus lowering the amount offeed-back voltage transferred from the anode P2 back over connection N to-the grid G1.' ':This

lowered feed-back potentialwill then result in a lower amplitude of oscillations which will besimi-J lar to that initially started the circuit. Conversely, if the amplitude falls below the'original assumed level, the gain of the pentode portion-of the tube is increased, thus restoring the voltage amplitude of the energy on grid G1 to the-pre determined level. generator functions to produce a constant amplitude of oscillations as thelosses of the circuit vary.

Fig. 5 shows still another embodiment of the invention which in most respects is quite similar to the circuit of Fig. 1. p

In Fig. v5, however, the grid G1 is constantly biased negatively-to a point on its grid-voltage .gridecurrent characteristic, such that. thevoltagef.

c5 Inthis way, the oscillation swing due vto'the alternating current voltage impressed on it will never allow grid current to flow. I The drawing of current by the grid, which is here avoided, ordinarily causes the generation harmonics, there is employed in Fig. '5 a resistor" of harmonics as is occasioned in the circuits of Figs. 1, 2, 3 and 4. To prevent the occurrence of Rs, by-passed by a condenser C5, ,which is common to the anode Plcathode K1 circuit of tube T1. The voltage drop across the resistor R8 is impressed on the grid G1 through the choke inacross the portion of the resistor R3, which is inductance L5. Putting" it another way, the grid G1 of tube T1 is here biased to function as a class A amplifier.

The tube T2 is shown in this Fig; 5 to be a variable mu 'screengrid pentode whosegrid' G'z is conductively coupled to the anode P1 of the 1 preceding tubethro'ugh an adjustable tap on resistance Ra -The adjustable tap is provided to allow the adjustment of thecircuit so that the amount of 'feed-back voltage from the anode P2 1 back to the-grid G1 over lead N is less than the.

bias'voltage across resistor Ra. The voltage drop across resistor R3 insures that the grid G'2 is so biased that the :tube T'zfunctions as a class A amplifien' In the event that the voltage drop cluded in the Gz cathode circuit of'tube T'z,

"Tz has been described as a variable mu tube,

is too small to insure class A operation of this tube,'an additional resistor-condenser combination similar tORa, C5 maybe included in the cathode circuit: of the tube T2. Although tube described in connection with Fig. 1. -It will be obvious, of course, that the tubes T1 and T2 can be combined within one' envelope to iorm a single tube such as theRCAtype 6F7.

: Fig. 6 is similar to Fig. 5,'except that the single tuned circuit comprising the inductance coil L1, L2, or L3, etc., andthecondenser C4, is

located in the anode circuit of tube T1 instead of in the grid circuit. The variable tap for con-. trolling the amount of feed-back is nowin the anode circuit of tube Tz instead ofin the grid circ"uit,-as shown in Fig; 5. A resistance R9 is included in the common circuit between the cathode of tube T'2 and the anode of tube T1. The voltage drop across this resistor provides the operating bias for thegrid of tube Tz. In all otherrespects, the circuit operation is substantially similar to what has been described above in connection with the other figures.

An inspection of all the rigures will show that it is only necessary to move'the single pole switch S to engage a single contact, in order to select any desired frequency range which may be char acteristic of a particular coil L1, L2, or L3, etc. This is possible because one terminal of each of these coils is permanently connected to the circuit while the other terminal is connected to a' contact of the switchingrnechanism S.

Although the inventionhas been described with particular reference 'to circuits employing two separate electron discharge device paths,

either in separate envelopes or combined in a single envelope, it is to be. distinctly understood that the invention is'not limited to such particular arrangements .since, if desired, any even' Outside of multiple of two electron discharge device paths may be employed.

' What is claimed is:

l. A two-terminal oscillation generator'comprising a pair of electron space paths, .each including a grid, an anode, and a cathode, an'electrically conductive connection extending from the anode of one path to the grid ofthe succeed- 7 ing path, a connection extending between said cathodes, said last connection being conductive solely for alternating current energy, and a feedback connection extending from the anode of said last path to the grid of the previous path for feeding back the alternating current energy in the anode circuit of said last path,a parallel tuned frequency controlling circuit for said system, said circuit being coupled between the grid and cathode of one of said space paths.

2. A two-terminal oscillation generator for the generation'of high frequency oscillations over a plurality of selective frequency ranges, comprising a pair of electron space paths, each including a grid, an anode, and a cathode, an electrically conductive connection extending from the anode of one path to the gridof the succeeding path, a connection extending between saidcathodes,

said connection being conductive solely for alternating current energy, and a feed-back connection including a condenser serially inserted therein extending from the anode of said last path to'the grid of the previous path for feeding back the alternating current energy in the anode cir-; cuit of said last path, a variable condenser coupled between the grid and cathode of one of said space paths, a plurality of inductance coils of different values, each having a terminal permanently connected, electrically, to one armature of said variable condenser and another terminal connected to a contact, a switch connected to the other armature of said variable condenser and;

adapted to engage any one of said contacts for 1 velopes.

5. A two-terminal oscillationv generator for the generation of high frequency oscillations over a plurality of selectivefrequency ranges, comprising an even plurality of electron space paths, each including a grid, an anode, and a cathode, a connection including a condenser serially inserted therein connecting together said cathodes, adirect current conductive connection extending from the anode of one pathto the grid of the succeeding path, and a capacitive feed-back con-' nection extending from the anode of said last path to the grid of the previous path for feeding back the alternating current energy in the anode circuit of said last path, a circuit for each path for maintaining the average grid potential at some definite negative value, a variable condenser,

manently connected, electrically, to one arma-. 'ture of said variable condenser and another terminal connected to a contact,'a switch connected :to,.-the; other; armature. of said variable condenser and adapted to engage any one of said contacts for selectively coupling any one of said induc tance coils in parallel relationship to said condenser, whereby said oscillation generator may generate oscillations of a frequency range determined by said condenser and'selected coil.

6. A system for the generation of high frequency oscillations comprising first and second electron discharge paths, each path having an anode, a grid, and electron emitting means, an

outputcircuit from the anode of said first pathconnected to the grid ofsaid second path, a parallel tuned frequency controlling circuit for saidsystem, said tuned circuit having an inductance and a condenser connected together inparallel arrangement, a connection from one terminal of said tuned circuit to the grid of said first discharge path, an electrically conductive connection from said same terminal to the anode of said second discharge path, a connection from the other terminal of said tuned circuit to the electron emitting means of said first path, a confirst discharge path is energized at a lower poten-v tial through the space of the second discharge path.

7. A system for the generation of high frequency oscillations comprising first and second electron discharge paths, each path having an anode, a grid and means for emitting electrons, an output circuit comprising a direct connection devoid of concentrated impedance from the anode of said first discharge path to the grid of said second discharge pathto energize same, and a feed-back circuit from the anode of said second discharge path to the grid of said first discharge path for feeding back the alternating current energy in theanode circuit of said second path, whereby said paths are in series relation, and a bias circuit for the grid of said second path including a resistor from said direct connection to the electron emitting means of said second path, whereby said direct connection functions simultaneously to energize said last grid and to provide a bias therefor, a connection between the electron emitting means of said two paths, 2; common. source of polarizing potential for said anodes, and a connection from the positive terminal of said source to one of said anodes, whereby the other anode is energized at a lower potential through the space of the path of the former anode. Y

8. A system for the generation of high frequency oscillations comprising first and second electron discharge paths, each path having an anode, a grid and means for emitting electrons,

an output circuit comprising a conductive con-.

conductive connection, to the electron emitting means of saidsecond' pathcwhereby said conduc- .tivezconnectionfunctions simultaneously to energize said last grid and to provideab-ias therefor,

and a tuned frequency controlling; circuit for said system, said tuned circuit comprising an a,

inductance and a condenser connected together in parallel arrangement, at least one of saidlast-elements being variable, a connection from. one ter minal of said tuned circuit to the grid of said first discharge path, and a connection from the;

other terminal of said tuned circuitto the elecv tron emitting means'of s'aidfirst path, a connection conductive solely for alternating current energy between the electron emitting means of both said paths, and a source of polarizing, poten-r, 1

tial for said anodes having one of. its terminals electron discharge paths, each path having an:

anode, a grid, and electron emitting means, an

output circuit from the anode of said first path connected to the grid of saidsecond path, a

parallel tunedfrequency controlling circuit for said system, a connection from-one terminal of:-

said tuned circuit to-the grid of "said first discharge path, an electrically conductive connection from said same terminal to the anod'eof' said second discharge path, a capacitive connec-- v tion from the other terminal of said tuned cir-gr cuit tothe electron emitting means of said first means of said first and second paths, and a path for direct current energy from said output'circuit to said last c'onnection,-a single source of polarizing potential for said anodes, a connection from the positive terminal of said source to said last terminal of said tuned circuit,and a connection from the negative terminal of said source to" the electron emitting means ofsaid first path, wherepath, a connection between theelectron emitting by the anode of said second discharge path is energized throughsaid tuned circuit, andthe second discharge path, said tuned circuit coma prisinga condenser and any one of a plurality of inductance coils of different values each hav-" ing a terminal permanently connected, electri-- cally, to one armature of said condenser and another terminal connected to a'contact,-a switch,

connected to the other armature of said condenser and adapted to engage'any one of said contacts for selectively coupling any. one of said inductance coils in parallel relationship to said condenser,

whereby said oscillationgenerator may. generate oscillations of a frequency range determined-by said condenser and selected coil. I

10. A two-terminal oscillation generator'for the generation of high frequency oscillations over a, plurality of, selective frequency ranges, comprising a pair of electron space paths within a single envelope, saidpaths being constituted by-a:

cathode, a first grid, an anode, a second cathode,

a second grid, and a second anode, in the order named; a capacitive, connection between saidv cathodes; a direct connection between said first anode and second grid; a resistance in series with an inductor connected between said first tion from said second anode to said first grid; a bias resistor between said first grid and said first cathode; a condenser between said first grid and '5 first cathode; a plurality of inductance coils of different values each having a terminal perma ne tly connected, le t ally, to one armatureiof said condenser and another terminal connected to a contact; a switch connected to the other armature of said condenser and adapted to engage any one of said contacts for selectively coupling any one of said inductance coils in parallel relationship to said condenser, whereby said oscillation generator may generate oscillations of a 30 current energy in the anode circuit of said second frequency range determined by said condense and the selected coil.

11. A two-terminal oscillator of high frequency oscillations comprising first and second electron discharge paths, each path having an anode, a grid and a cathode, an output circuit comprising a conductive connection from the anode of said first discharge path to the grid of said second discharge path to energize same, and a feed-back circuit from the anode of said second discharge path to the grid of said first discharge path for feeding back substantially all of the alternating charge path, and a connection from the other terminal of said tuned circuit to the cathode of said first path, a connection between said cathodes, said connection being conductive solely to alternating current, and a source of polarizing potential for said anodes.

RUDOLPH H. SIEMENS. m; 

